This invention relates to methods of forming a layer on a substrate using a vapor deposition process, particularly a multi-cycle atomic layer deposition (ALD) process, using one or more Group IIA metal precursor compounds and optionally other metal (e.g., titanium) precursor compounds, typically in the presence of one or more reaction gases. The precursor compounds and methods are particularly suitable for the formation of strontium and/or barium titanate dielectric layers on semiconductor substrates or substrate assemblies.
Capacitors are the basic energy storage devices in random access memory devices, such as dynamic random access memory (DRAM) devices and ferroelectric memory (FERAM) devices. They consist of two conductors, such as parallel metal or polysilicon plates, which act as the electrodes (i.e., the storage node electrode and the cell plate capacitor electrode), insulated from each other by a dielectric material.
The continuous shrinkage of microelectronic devices such as capacitors over the years has led to a situation where the materials traditionally used in integrated circuit technology are approaching their performance limits. Silicon (i.e., doped polysilicon) has generally been the substrate of choice, and silicon dioxide (SiO2) has frequently been used as the dielectric material to construct microelectronic devices. However, when the SiO2 layer is thinned to 1 nm (i.e., a thickness of only 4 or 5 molecules), as is desired in the newest microelectronic devices, the layer no longer effectively performs as an insulator due to the tunneling current running through it. This SiO2 thin layer deficiency has lead to the search for improved dielectric materials.
High quality dielectric layers containing Group IIA metal titanates such as SrTiO3, BaTiO3, and (Ba1xe2x88x92xSrx)TiO3 are of interest to the semiconductor industry as they exhibit higher permitivities than do dielectric layers containing SiO2. Consequently, the semiconductor industry has been extensively evaluating strontium, barium, and titanium precursor compounds that can be used in vapor deposition processes.
Chemical vapor deposition (CVD) is a continuous, single step vapor deposition process that can be used to deposit dielectric films (i.e., layers) having excellent conformality and is therefore of significant interest in making strontium and barium titanate thin films. In CVD, excellent conformality is achieved when the process is carried out at a temperature low enough that the surface reactions are the rate-limiting step in the film growth. At higher temperatures the precursor compound transformation becomes the limiting factor, causing a degradation of the conformality.
Atomic layer deposition (ALD) is a more sophisticated vapor deposition process capable of forming even higher quality dielectric layers due to the self-limiting film growth and the optimum control of atomic-level thickness and film uniformity. Using the ALD process, several sequential process cycles arc employed to deposit the layer on the substrate one monolayer at a time per cycle until the desired layer thickness is achieved. For each cycle of the ALD process, vapors of one or more precursor compounds are pulsed into the deposition chamber and are chemisorbed onto the substrate. Typically, one or more vaporized reaction gases (e.g., water vapor) are pulsed into the deposition chamber to react with the chemisorbed precursor compound(s) and cause the deposition of the desired layer onto the substrate. With the ALD process, more reactive precursors can be used, without the problem of gas-phase reactions, resulting in lower temperature requirements at the substrate.
Vehkamxc3xa4ki et al., xe2x80x9cGrowth of SrTiO3 and BaTiO3 Thin Films by Atomic Layer Deposition,xe2x80x9d Electrochemical and Solid-State Letters, 2(10):504-506 (1999) describe thin films of SrTiO3 and BaTiO3 deposited by ALD processes making use of a novel class of strontium and barium precursors, i.e., their cyclopentadienyl compounds, together with titanium tetraisopropoxide and water. Prior to their discovery, Vehkamxc3xa4ki et al. state that the selection of strontium and barium precursor compounds has been limited to their xcex2-diketonate compounds that do not react with water or oxygen at temperatures low enough for the self-limiting growth mechanism of ALD processes.
The search continues for sufficiently volatile Group IIA metal precursor compounds, especially strontium and/or barium precursor compounds, to employ successfully in vapor deposition processes, particularly ALD processes, to form, for example, strontium titanate, barium titanate, and barium-strontium titanate dielectric layers.
This invention provides vapor deposition processes, and particularly a multi-cycle atomic layer deposition (ALD) processes, for forming a metal-containing layer on a substrate using one or more Group IIA metal diorganoamide precursor compounds, and optionally one or more other metal-containing precursor compounds (e.g., titanium precursor compounds) and/or one or more reaction gases, such as water vapor. Preferably, the formed layer is an oxide layer, which can be used as a dielectric layer. Examples of such layers are primarily composed of a Group IIA metal titanate, such as strontium titanate, barium titanate, or barium-strontium titanate.
In one embodiment, the present invention provides a method of forming a layer on a substrate, such as is used in the manufacturing of a semiconductor structure. The method includes: providing a substrate (preferably a semiconductor substrate or substrate assembly such as a silicon wafer); providing a vapor including one or more Group IIA metal precursor compounds of the formula M(NRRxe2x80x2)2, wherein R and Rxe2x80x2 are each independently an organic group (preferably having 1 to 10 carbon atoms, which are optionally replaced by or substituted with silicon, oxygen, and/or nitrogen atoms and/or groups containing such atoms), and M is selected from the group consisting of barium, strontium, calcium, and magnesium (preferably, strontium and barium); and directing the vapor to the substrate to form a metal-containing layer (preferably, a metal oxide layer, which is useful as a dielectric layer) on a surface of the substrate using an atomic layer deposition process that includes a plurality of deposition cycles.
In another embodiment, the present invention provides a method of forming a layer on a substrate. The method includes: providing a substrate (preferably a semiconductor substrate or substrate assembly such as a silicon wafer); providing a vapor including one or more Group IIA metal precursor compounds of the formula M(NRRxe2x80x2)2 (Formula I), wherein R and Rxe2x80x2 are each independently an organic group (preferably having 1 to 10 carbon atoms, which are optionally replaced by or substituted with silicon, oxygen, and/or nitrogen atoms and/or groups containing such atoms), and M is selected from the group consisting of barium, strontium, calcium, and magnesium (preferably, strontium and barium); providing one or more reaction gases (preferably, water vapor); and directing the vapor including the one or more Group IIA metal precursor compounds and the one or more reaction gases lo the substrate to form a metal-containing layer (preferably, a metal oxide layer, which is useful as a dielectric layer) on a surface of the substrate using an atomic layer deposition process that includes a plurality of deposition cycles a plurality of deposition cycles.
In yet another embodiment, the present invention provides a method of forming a layer on a substrate. The method includes: providing a substrate (preferably a semiconductor substrate or substrate assembly such as a silicon wafer) within a deposition chamber; providing a vapor including one or more Group IIA metal precursor compounds of the formula M(NRRxe2x80x2)2 (Formula I), wherein R and Rxe2x80x2 are each independently an organic group (preferably having 1 to 10 carbon atoms, which are optionally replaced by or substituted with silicon, oxygen, and/or nitrogen atoms and/or groups containing such atoms), and M is selected from the group consisting of barium, strontium, calcium, and magnesium (preferably, strontium and barium); providing one or more reaction gases; and directing the one or more reaction gases toward the substrate with the chemisorbed species thereon to form a metal-containing layer on one or more surfaces of the substrate. Preferably, one or more inert carrier gases are introduced into the chamber after the vapor including the one or more compounds of Formula I, after the one or more reaction gases, or after both the vapor and the reaction gases.
Optionally, the methods of the present invention can also further include a step of providing a vapor including one or more metal-containing precursor compounds other than the compounds of Formula I and directing this vapor to the substrate to form a metal-containing layer. Such compounds are preferably titanium compounds, such as those of the formula Ti(AR1x)4, wherein: A is O, N, C(O), or OC(O); and R1 is a (C1-C10)alkyl group, wherein two of the R1 alkyl groups are optionally joined together to form an alkylene group; and n=1 or 2. Using such additional precursor compounds, mixed-metal oxides can be formed such as strontium titanate, barium titanate, and barium-strontium titanate.
The precursor compounds can be directed to the substrate together (e.g., substantially simultaneously) or separately. They can be directed to the substrate in the same cycle or in separate (e.g., alternating) cycles. They can all be directed to the substrate before directing one or more reaction gases to the substrate.
In a preferred embodiment, methods of the present invention include: providing a vapor including one or more precursor compounds of Formula I and directing this vapor to the substrate and allowing the one or more compounds to chemisorb to one or more surfaces of the substrate; providing one or more reaction gases and directing the one or more reaction gases to the substrate with the chemisorbed species thereon; providing a vapor including one or more precursor compounds other than those of Formula I and directing this vapor to the substrate and allowing the one or more compounds to chemisorb to one or more surfaces of the substrate; providing one or more reaction gases and directing the one or more reaction gases to the substrate with the chemisorbed species thereon to form a metal-containing layer on one or more surfaces of the substrate. Preferably, the methods include purging excess vapor including the one or more precursor compounds from the deposition chamber after chemisorption of the compounds onto the substrate. These steps typically form a cycle that is repeated at least once, and often hundreds of times.
In another embodiment, the present invention provides a method of manufacturing a memory device structure. The method includes: providing a substrate (preferably a semiconductor substrate or substrate assembly such as a silicon wafer) having a first electrode thereon; providing one or more Group IIA metal precursor compounds of the formula M(NRRxe2x80x2)4, wherein R and Rxe2x80x2 are each independently an organic group and M is selected from the group consisting of barium, strontium, calcium, and magnesium; vaporizing the one or more precursor compounds; directing the one or more vaporized precursor compounds to the substrate to chemisorb the compounds on the first electrode of the substrate; providing one or more reaction gases; directing the one or more reaction gases to the substrate with the chemisorbed compounds thereon to form a dielectric layer on the first electrode of the substrate; and forming a second electrode on the dielectric layer.
In yet another embodiment, the present invention provides an atomic layer vapor deposition apparatus that includes: a deposition chamber having a substrate (preferably a semiconductor substrate or substrate assembly such as a silicon wafer) positioned therein; one or more vessels that include one or more Group IIA metal precursor compounds of the formula M(NRRxe2x80x2)2, wherein R and Rxe2x80x2 are each independently an organic group and M is selected from the group consisting of barium, strontium, calcium, and magnesium.
xe2x80x9cSubstratexe2x80x9d as used herein refers to any base material or construction upon which a metal-containing layer can be deposited. The term xe2x80x9csubstratexe2x80x9d is meant to include semiconductor substrates and also include non-semiconductor substrates such as films, molded articles, fibers, wires, glass, ceramics, machined metal parts, etc.
xe2x80x9cSemiconductor substratexe2x80x9d or xe2x80x9csubstrate assemblyxe2x80x9d as used herein refers to a semiconductor substrate such as a metal electrode, base semiconductor layer or a semiconductor substrate having one or more layers, structures, or regions formed thereon. A base semiconductor layer is typically the lowest layer of silicon material on a wafer or a silicon layer deposited on another material, such as silicon on sapphire. When reference is made to a substrate assembly, various process steps may have been previously used to form or define regions, junctions, various structures or features, and openings such as capacitor plates or barriers for capacitors.
xe2x80x9cLayerxe2x80x9d as used herein refers to any metal-containing layer that can be formed on a substrate from the precursor compounds of this invention using a vapor deposition process. The term xe2x80x9clayerxe2x80x9d is meant to include layers specific to the semiconductor industry, such as xe2x80x9cbarrier layer,xe2x80x9d xe2x80x9cdielectric layer,xe2x80x9d and xe2x80x9cconductive layer.xe2x80x9d (The term xe2x80x9clayerxe2x80x9d is synonymous with the term xe2x80x9cfilmxe2x80x9d frequently used in the semiconductor industry.) The term xe2x80x9clayerxe2x80x9d is also meant to include layers found in technology outside of semiconductor technology, such as coatings on glass.
xe2x80x9cDielectric layerxe2x80x9d as used herein is a term used in the semiconductor industry that refers to an insulating layer (sometimes referred to as a xe2x80x9cfilmxe2x80x9d) having a high dielectric constant that is typically positioned between two conductive electrodes to form a capacitor. For this invention, the dielectric layer contains a Group IIA metal compound where preferably the compound is a titanate, including barium titanate, strontium titanate, barium-strontium titanate, calcium titanate and magnesium titanate.
xe2x80x9cPrecursor compoundxe2x80x9d as used herein refers to a Group IIA metal compound capable of forming (typically in the presence of a reaction gas) a metal-containing layer on a substrate in a vapor deposition process. The resulting Group IIA metal-containing layers are typically oxide layers, which are useful as dielectric layers.
xe2x80x9cDeposition processxe2x80x9d and xe2x80x9cvapor deposition processxe2x80x9d as used herein refer to a process in which a metal-containing layer is formed on one or more surfaces of a substrate (e.g., a doped polysilicon wafer) from vaporized precursor compound(s). Specifically, one or more metal precursor compounds are vaporized and directed to one or more surfaces of a heated substrate (e.g., semiconductor substrate or substrate assembly) placed in a deposition chamber. These precursor compounds form (e.g., by reacting or decomposing) a non-volatile, thin, uniform, metal-containing layer on the surface(s) of the substrate. For the purposes of this invention, the term xe2x80x9cvapor deposition processxe2x80x9d is meant to include both chemical vapor deposition processes (including pulsed chemical vapor deposition processes) and atomic layer deposition processes.
xe2x80x9cChemical vapor depositionxe2x80x9d (CVD) as used herein refers to a vapor deposition process wherein the desired layer is deposited on the substrate from vaporized metal precursor compounds and any reaction gases used within a deposition chamber with no effort made to separate the reaction components. In contrast to a xe2x80x9csimplexe2x80x9d CVD process that involves the substantial simultaneous use of the precursor compounds and any reaction gases, xe2x80x9cpulsedxe2x80x9d CVD alternately pulses these materials into the deposition chamber, but does not rigorously avoid intermixing of the precursor and reaction gas streams, as is typically done in atomic layer deposition or ALD (discussed in greater detail below). Also, for pulsed CVD, the deposition thickness is dependent on the exposure time, as opposed to ALD, which is self-limiting (discussed in greater detail below).
xe2x80x9cAtomic layer depositionxe2x80x9d (ALD) as used herein refers to a vapor deposition process in which numerous consecutive deposition cycles are conducted in a deposition chamber. Typically, during each cycle the metal precursor is chemisorbed to the substrate surface; excess precursor is purged out; a subsequent precursor and/or reaction gas is introduced to react with the chemisorbed layer; and excess reaction gas (if used) and by-products are removed. As compared to the one cycle chemical vapor deposition (CVD) process, the longer duration multi-cycle ALD process allows for improved control of layer thickness by self-limiting layer growth and minimizing detrimental gas phase reactions by separation of the reaction components. The term xe2x80x9catomic layer depositionxe2x80x9d as used herein is also meant to include the related terms xe2x80x9catomic layer epitaxyxe2x80x9d (ALE) (see U.S. Pat. No. 5,256,244 (Ackerman)), molecular beam epitaxy (MBE), gas source MBE, organometallic MBE, and chemical beam epitaxy when performed with alternating pulses of precursor compound(s), reaction gas and purge (i.e., inert carrier) gas.
xe2x80x9cChemisorptionxe2x80x9d as used herein refers to the chemical adsorption of vaporized reactive precursor compounds on the surface of a substrate. The adsorbed species are irreversibly bound to the substrate surface as a result of relatively strong binding forces characterized by high adsorption energies ( greater than 30 kcal/mol), comparable in strength to ordinary chemical bonds. The chemisorbed species are limited to the formation of a monolayer on the substrate surface. (See xe2x80x9cThe Condensed Chemical Dictionaryxe2x80x9d, 10th edition, revised by G. G. Hawley, published by Van Nostrand Reinhold Co., New York, 225 (1981)). The technique of ALD is based on the principle of the formation of a saturated monolayer of reactive precursor molecules by chemisorption. In ALD one or more appropriate reactive precursor compounds are alternately introduced (e.g., pulsed) into a deposition chamber and chemisorbed onto the surfaces of a substrate. Each sequential introduction of a reactive precursor compound is typically separated by an inert carrier gas purge. Each precursor compound co-reaction adds a new atomic layer to previously deposited layers to form a cumulative solid layer. The cycle is repeated, typically for several hundred limes, to gradually form the desired layer thickness. It should be understood, however, that ALD can use one precursor compound and one reaction gas.